Carbon dioxide is a well-known gas, which is present in the atmosphere. It is released to the atmosphere in large amounts by fermentation processes, limestone calcination, and all forms of combustion processes of carbon and carbon compounds. In the recent decades, the attention in respect of said emission has been rising, because of the environmental problem due to future climate change via Greenhouse effect. Consequently, extensive work has been performed over the years in order to develop processes for the removal of carbon dioxide from combustion gases. If possible, a subsequent recovery of carbon dioxide may make those processes economical feasible.
Various methods for removal of a gaseous component from a gas stream are known in the art. Especially, absorption has been mentioned as a suitable method for removal of components from gaseous waste streams. In U.S. Pat. No. 3,266,220 it was proposed to remove carbon dioxide from gaseous mixtures by the utilization of solvents having a selective solubility of carbon dioxide. As examples of selective solvents are mentioned water, methyl alcohol, acetone and propylene carbonate.
It is well-known that the triple point for pure carbon dioxide is situated at −56.6° C. and 5.2 bar. This means that carbon dioxide cannot be found as a liquid at atmospheric pressure irrespective of the temperature. In order to obtain a liquid a temperature above −56.6° C. and a pressure of at least 5.2 bar must be applied.
A method for liquefaction of carbon dioxide from fermentation of alcohol or from other gas sources by condensation following compression is disclosed in European patent application EP 1308502. In this method, the condensation takes place preferably at −20° C. to −55° C. and at a pressure in the range of 19-20 bar. However, no further effort for recovery of uncondensed carbon dioxide is mentioned in said script.
The object of the present invention is to provide a method for recovery of carbon dioxide from a CO2-containing gas.
Surprisingly, the present inventor has found that an improved method for recovery of carbon dioxide from a gas may be obtained by a novel two-step method. By combining an initial condensation of the gas to be treated with a subsequent absorption of the gaseous carbon dioxide, which did not condense in the first step, it is possible to recover carbon dioxide at much higher yields than known in the art and in a financially more feasible way.